The optical system of the eye is composed by refractive elements (cornea and lens) and aqueous and vitreous humors. The crystalline lens of the eye is the second lens in the eye, behind the cornea and the iris. In the emmetropic eye the optical power of the cornea and crystalline lens are such that the optical image is projected sharply on the retina. In the young eye the crystalline lens can alter its shape to accommodate near and far objects. This capability is lost with age (a condition called presbyopia). Also, the normal lens is transparent. Also with aging, the crystalline lens opacifies (a condition called cataract).
The crystalline lens can be replaced by an artificial intraocular lens (IOL) to correct for refractive errors in non-emmetropic eyes, and more commonly, to correct for cataract. Recently, intraocular lenses that aim at restoring the accommodation capability of the eye (i.e. correcting presbyopia) have been proposed. These accommodating IOLs (A-IOLs) are intended to use of the accommodative forces transmitted from the ciliary muscle to the lens by the zonulae and the lens capsule, to shift axially or laterally one of more elements, or reshape the geometry of the lens.
Most intraocular lens designs have a central optical zone and two or more haptics to hold the lens in place inside the capsular bag, and to guarantee IOL stability and centration. While intracapsular cataract surgery has proved safe and in most cases uneventful, post-operative problems may arise associated to capsular fibrosis that results from anterior capsule epithelial cells proliferation and migration. Capsular fibrosis may result in posterior capsule opacification (and the need of a secondary surgery) and capsular bag contraction and IOL misalignment.
An alternative IOL design aimed at preventing the effects of capsular fibrosis and opacification is that of the so-called “bag in the lens”. In this technique the peripheral groove of the lens allows holding the anterior and posterior capsulorhexis (surgically performed window edges) of the capsular bag.
Haptic design is of particular relevance in A-IOLs, as they require the transmission of forces from the accommodative implant into the lens. The mechanism of operation of several accommodating IOL designs requires the capsular bag to operate similarly to that in the intact eye, although it is likely that fibrosis following cataract surgery will compromise these mechanisms.
An identified problem of several accommodating IOLs is the lack of a strong connection with the capsular bag that is needed for adequate transfer of forces from the ciliary muscle to the action mechanism of the lens; this is the case of the two optic accommodative lens system disclosed in patent document U.S. Pat. No. 7,150,760.
Some A-IOLs require that the connection between the haptics and the periphery of the capsular bag is produced by natural fibrosis occurring during the weeks following implantation. However, this uncontrolled process may result in a limitation of the shifting or reshaping mechanism of the A-IOL.
Some patent documents disclose haptic devices that depend on the fibrosis process, such as U.S. Pat. No. 6,193,750. US-2011/0307058 proposes the zonular capture haptic, which favors the fusion of the capsular bag to the haptics, assisted by the natural process of fibrosis. This approach requires two surgical acts separated by days, in which the haptic platform and the A-IOL are implanted, respectively. Relying on the natural fibrosis for the engaging the A-IOL to the capsular bag has several drawbacks, including the duration of the process, uncertainty in the A-IOL alignment, and the final outcome of the engagement. Nevertheless, engagement of the haptic to the capsule is critical in several A-IOL designs.
Patent document US-2003/0204254 proposes mechanical engagement of the lens haptic (or lens periphery) to the edge of the capsulorhexis using mechanical blocking arms or clasps. A drawback of such a mechanical attachment to the capsule is the potential tearing or rupture of the capsule.
An alternative to the use of mechanical capsule-IOL engagement system is the use of bio-adhesives. Bio-adhesive materials are increasingly used in medicine for tissue repair in surgery, drug delivery, or attachment of prosthetic devices. For example, patent document US-2008/0140192 discloses the use of a reversible thermo-responsive adhesive substance for attaching microelectronic retinal implants to the retinal tissue. This particular polymer has the property of becoming adhesive to cells above a critical temperature, 32°, in aqueous environments.
The use of bio-adhesive polymers has been recognized as advantageous in applications where an intraocular lens requires a firm attachment to the capsular bag to transmit the forces of the accommodative plant into an A-IOL mechanism. Patent document WO-96/35398 suggests thermal adhesion of the peripheral part of an IOL (coated with an adhesive material) to the anterior capsulorhexis, by increasing temperature with a laser to produce thermal welding of the IOL material and the capsular bag tissue.
Patent document US-2011/0029074 proposes the use of a thermo-reversible material for applications in intraocular surgery, including A-IOL implantation and stunt implantation in glaucoma. In this document they also recognize the need for effectively translating the ocular forces of the natural accommodative mechanism to maximize the accommodation amplitude of A-IOLs, and propose the use of polymeric systems that may modify their adhesive properties in response to changes of the physical and chemical characteristics of the physiological medium. In particular, they propose the use of a thermo-reversible adhesive polymer coating the surface of certain areas of a haptic structure (and possibly the surface of the IOL) to favor the adhesion of the system to the capsular bag. The thermo-adhesive polymer would exhibit adhesive properties at body temperature. Irrigation with cold or room temperature solution during the surgical procedure, or possibly for explanation could produce detachment of the IOL/haptic from the capsular bag. Although pNIPAM polymer is described as a biocompatible non-toxic substance to neural tissue or cultured cells, its intraocular non-toxicity has never been proven. The non-polymerized form NIPAM has been proven toxic to neural tissue. On the other hand, the dynamical properties of the pNIPAM adhesive when deposited as a thin layer across the capsulorhexis have not been proven and it is not clear whether it may remain for sufficient time to produce a thermo-adhesive response.
The use of photo-chemically induced bonding processes is also known. The use of localized light delivery is particularly well suited intraocularly, as done in several procedures, including retinal photocoagulation or laser trabeculoplasty in glaucoma. The use of localized irradiation in internal body organs is generally performed by the use of catheters for visualization, sensing or treatment. For example, as described in patent document U.S. Pat. No. 6,106,550, light can be conducted through a fiber and emitted from its end into the surroundings for purposes of, among others, illumination or for cutting tissue with a laser beam.
Also, a photo-activated process is used in corneal collagen cross-linking for the treatment of keratoconus by tissue stiffening. In this procedure, formation of inter- and intra-fibrillar bonding is produced by the instillation of a photosensitizer (typically a riboflavin-containing solution) and irradiation with UVA light. Corneal collagen photo-cross-linking has also been demonstrated with other photosensitizers, such as Rose Bengal, and irradiation with green light. One of the advantages of the use of Rose Bengal is that it is an FDA-approved compound of widespread use in ophthalmology, for example in dry eye staining tests. In addition, intracapsular use of Rose Bengal has proved non-toxic in rabbit eye models. The use of photosensitizers and photo-activation is described in U.S. Pat. No. 7,331,350 to produce heat-free bonding of damaged tissue for repair, therefore replacing sutures of staples. These photochemical tissue-bonding methods include the application of a photosensitizer to tissue (i.e. the cornea) followed by irradiation with electromagnetic energy to produce a tissue-tissue seal, in the absence of an exogeneously supplied source of cross-linkable structure. It is thought that in photochemical bonding that activation of the photoinitiator by light absorption produces structural changes in the amino acids of the proteins of the tissue and formation of covalent bonds between collagen molecules on opposing surfaces of the two tissues in contact.
Therefore, there is a need for an accommodating intraocular lens that can be securely fixed to the capsular eye by means of a non-toxic process and, at the same time, providing sufficient resistance to rupture.